Optimal tire size for 17.0mm internal width (21.5mm external)

[rides4beer]

Looking at a set of Novatec Jetfly wheels, 17.0mm internal/21.5mm external. I'm thinking 23c Continental GP4000sII. I realize that 25c will fit, but which will be the best fit for these wheels?

My stock wheels have 25c tires and ride/handle great, but they're also 19mm internal.

[Marin]

Optimal for what? You can mount anything from 19 to 40mm and more on those rims. The ride will mostly depend on tire type and pressure, rim width is actually quite unimportant.

[moyboy]

sounds like 25

[alcatraz]

Hows the road quality around there? How much do you weigh?

If you're heavier or have bad roads go a bit wider. Even 28mm if you need to. On narrow internal width they don't balloon as much as on wide rims. Some brands balloon a lot less than others so better double check your frame clearance.

You wanna run a tire wide enough so you can run around 90-100psi without getting pinch flats. For bad roads better go down another 5-10 psi.

You can run one step wider in the rear.

If you're light and roads are fairly smooth you could run 23c. Also your preference comes into play. Do you like it nice and rigid with lots of road feel, high pressure-narrow tire, or would you like to get some more cushioning for tired joints and limbs, then go a step or two wider.

The fastest tire is sometimes the one that feels good. That doesn't necessarily mean 120psi 23mm bouncing around on every bump. Something that lets you keep the power on at all time is fast. Gp4k have a good balance of rr/puncture resistance/weight. They balloon quite a lot so a 23c is essentially a 24c, 25~26, 28~30.

[rides4beer]

Optimal for what? You can mount anything from 19 to 40mm and more on those rims. The ride will mostly depend on tire type and pressure, rim width is actually quite unimportant.

Speed/handling mostly, comfort is of course a concern as well. I'm new to riding, but like to go fast and we have some good descents around here, so I want to make sure they handle well. Just figured that while multiple sizes would fit, one or the other would possibly fit/perform better.

sounds like 25

The 25s that are on my stock wheels ride and handle well, just wasn't sure if losing 2mm in rim width would make a difference. From what I'm reading 25s are what most people are using these days, but the rims have also gotten wider.

[rides4beer]

Hows the road quality around there? How much do you weigh?

If you're heavier or have bad roads go a bit wider. Even 28mm if you need to. On narrow internal width they don't balloon as much as on wide rims. Some brands balloon a lot less than others so better double check your frame clearance.

You wanna run a tire wide enough so you can run around 90-100psi without getting pinch flats. For bad roads better go down another 5-10 psi.

You can run one step wider in the rear.

If you're light and roads are fairly smooth you could run 23c. Also your preference comes into play. Do you like it nice and rigid with lots of road feel, high pressure-narrow tire, or would you like to get some more cushioning for tires joints and limbs, then go a step or two wider.

Roads aren't too bad, most of my routes are mostly smooth, few bad patches here and there that I can usually avoid, my current 25s on 19mm rims ride great, so maybe stay with 25s? I'm 6' 185lbs and have some good power (ultra runner with strong legs just getting into cycling). I ride a Fuji Transonic, pretty stiff carbon aero frame, def feel every bump, but I don't mind it. I like to feel connected and want to make sure I have have good handling and grip.

[rides4beer]

The fastest tire is sometimes the one that feels good. That doesn't necessarily mean 120psi 23mm bouncing around on every bump. Something that lets you keep the power on at all time is fast. Gp4k have a good balance of rr/puncture resistance/weight. They balloon quite a lot so a 23c is essentially a 24c, 25~26, 28~30.

Current tires are Vittoria Zaffiro Pros, but I've read good things about the GP4Ks so figured I'd go with those. Sounds like staying with 25s might be my best bet. Just wanted to make sure that I didn't need to step down a tire size with a narrower rim.

[alcatraz]

Vittora is on one end of the spectrum while Continental is on the opposite side.

I'm talking about measured width.

If you use Vittoria I suggest 28c for your weight, at the very least in the rear. If you go continental you could be ok with 25c. Or 23/25, maybe better 25/28.

If you get some wide rims one day you can reap the benefits of an aero tire fit (~30mm wide rims for your weight) and potentially going down a tire size (because of ballooning), 28 to 25c as an example. All that matters is the measured real width, not what's written on the tire.

Also 100psi is faster than 120. 90 is faster than 100 on most roads.

[AJS914]

Just remember that 23mm GP4000s are basically 25mm wide. They measure 25mm on my 15C rims and 26mm on 19mm rims.

You can refer to Hambini's test. Look at the tire width section. a 23mm GP4 is a few watts faster at 30km/hr.

Roads are rough where I live so I'd go wider with a lower pressure if my bike allowed it. I also don' t need to optimize for those last 3 watts. On rough roads, wider tires at a lower pressure could result in less rolling resistance which trumps those 3 aero watts.

[rides4beer]

Vittora is on one end of the spectrum while Continental is on the opposite side.

I'm talking about measured width.

If you use Vittoria I suggest 28c for your weight, at the very least in the rear. If you go continental you could be ok with 25c. Or 23/25, maybe better 25/28.

If you get some wide rims one day you can reap the benefits of an aero tire fit (~30mm wide rims for your weight) and potentially going down a tire size (because of ballooning), 28 to 25c as an example. All that matters is the measured real width, not what's written on the tire.

Also 100psi is faster than 120. 90 is faster than 100 on most roads.

Sorry, just meant that those are what I'm riding on now, they came with the bike. I haven't had any issues with them, but they will be staying on the stock wheels as backups. Getting the Continentals for the new wheels.

I appreciate all of the advice, I've only been riding a few months, still learning a lot.

Just remember that 23mm GP4000s are basically 25mm wide. They measure 25mm on my 15C rims and 26mm on 19mm rims.

You can refer to Hambini's test. Look at the tire width section. a 23mm GP4 is a few watts faster at 30km/hr.

Roads are rough where I live so I'd go wider with a lower pressure if my bike allowed it. I also don' t need to optimize for those last 3 watts. On rough roads, wider tires at a lower pressure could result in less rolling resistance which trumps those 3 aero watts.

So probably safe to go with the 25s, see what the measure at and play with the pressure to see what works for me. I should measure the Vittorias and see what the actual tire width section is.

[pdlpsher1]

Tires will stretch and get wider with time. The Conti will grow wider by about 1mm in two weeks. My 25mm on 17C rim measures 27mm after stretching. When new they are 26mm. Also tires will measure differently on different parts of the tire. I take five measurements and average them. I use a digital veneer caliper.


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[Hexsense]

You can't be aero optimized on that rim anyway.
21.5mm external width means your tire must be less than 21mm mounted to be aero optimized. Like what? 18c?
And you wouldn't buy that kind of wheel expecting them to be aero.

So, with matching external width to tire width out of question. Then consider internal width.
Your internal width ride fine with 21c and up. But 17mm internal width provide less stable platform for your tire than something wider. If you get 28c and up, you may found that you can drop pressure a bit more riding straight line but it feel too squishy in corner because of less stable rim base. So you may need to overinflate a bit for 28c and up just to feel right in corner.

21c-25c are what work best for your rim then.

[rides4beer]

Tires will stretch and get wider with time. The Conti will grow wider by about 1mm in two weeks. My 25mm on 17C rim measures 27mm after stretching. When new they are 26mm. Also tires will measure differently on different parts of the tire. I take five measurements and average them. I use a digital veneer caliper.


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So a 23 will end up more like 25. I should probably pick up a caliper, always like an excuse to buy tools.

You can't be aero optimized on that rim anyway.
21.5mm external width means your tire must be less than 21mm mounted to be aero optimized. Like what? 18c?
And you wouldn't buy that kind of wheel expecting them to be aero.

So, with matching external width to tire width out of question. Then consider internal width.
Your internal width ride fine with 21c and up. But 17mm internal width provide less stable platform for your tire than something wider. If you get 28c and up, you may found that you can drop pressure a bit more riding straight line but it feel too squishy in corner because of less stable rim base. So you may need to overinflate a bit for 28c and up just to feel right in corner.

21c-25c are what work best for your rim then.

I don't think I'll be going with 28s, so 25s with proper inflation should still handle well on these rims?

[AJS914]

I think a 25mm tire sounds perfect.

This site also measures height and width of the tires they test:

https://www.bicyclerollingresistance.com/

[Bigger Gear]

On a 17mm internal rim, the Conti GP4000sii 23C will be 25.5ish. The 25C will be 27.5ish and the 28C will be 30.5ish. Another thing is that the Conti tires are tall for stated size. I could not run a GP4000Sii in a 25C on a rim 17mm or larger on my Colnago C60 because it would be too close to the fork crown. But, I could use a Vittoria Corsa G+ in 25mm width on a 20.5mm inner no problem. So for the OP, make sure you can get a 25C GP4000Sii to fit before buying them.

And Hexsense is on to something important, having the inner width significantly more narrow than the tire width creates a very different riding tire. I've played around putting a 28C Conti on a 15mm innner width rim, and on a 20.5mm inner width rim with all other variables kept the same. The narrow rim gives the tire much more of a lightbulb shape and the feeling under hard cornering is much more vague. And climbing steep grades out of the saddle, the front wheel always feels more flexy. This is the effect of the very round sidewall on the 15mm rim vs a much more vertical sidewall on the 20.5mm rim.

For the wheels I have that are 17mm innner I use either 23C Conti or 25C Vittoria. I'm 76 kg (168 lbs ish) and ride a mix of perfect tarmac to rough chipseal. For that setup I'd use 80 PSI front/85 rear. Seems to be enough to avoid pinch flats but still corner well and not feel "squishy" when sprinting or steep climbing.